Sprinkler systems for fire protection of buildings require valves which shut-off various portions of the sprinkler system to allow work to be done on the system without the flow of water. Traditionally, these valves have represented a serious fire protection problem as they can be accidently or purposely left in the closed position, which deprives the sprinkler system of the water that would be used to suppress a fire. To combat this possibility, the National Fire Codes require that valves for fire protection sprinkler systems be open stem and yoke (OS&Y) valves. This design enables one to visually verify whether the valve is fully open or not.
Many property insurance authorities also require that these valves be electrically monitored in such a way that a "supervisory signal" is transmitted whenever the valve is not in the fully open position. This signal is received by a continuous monitoring station at a remote location. This requirement gave rise to the need for valve-status, supervision switches.
For the past thirty years, valve-status, supervisory switches have consisted of a simple electro-mechanical switch connected to the stem of the valve through a mechanical linkage. Over the years, numerous incremental improvements have been made in the mechanical linkage and the ease of manufacturing these switches. However, the devices have not changed in concept--a mechanical linkage tripping on electro-mechanical switch. The problems with this design concept have persisted regardless of these incremental improvements. The mechanical linkage requires consistently close tolerances between the yoke and stem of the OS&Y valve while the mounting methods require large tolerances to accommodate the wide variations in the sizes of valves and the castings from which they are constructed. Consequently, valve-status, supervision switches have been a constant source of system failures as they rapidly come out of adjustment and render incorrect status indications; fail to report a closure when valves are closed; fail to report an opening when valves are opened; report closure when the valve is open; and, report an open condition when the valve is actually closed. The solution to these failures is almost always the adjustment of the mounting brackets to allow the mechanical linkage to assume the correct position. However, this adjustment often renders the opposite state of the valve unreported.